1. Field of the Invention
The present invention relates to footwear. The invention concerns, more particularly, elements that protrude from a footwear sole to provide dynamic traction.
2. Description of Background Art
The game of golf is one of the oldest international sports and has its formal origins in the 16th century at The Royal and Ancient Golf Club at St. Andrews, located in Scotland. During the ensuing centuries, the game of golf has gained and maintained a populous following due to inherent challenges of the game, a prestigious reputation, and its suitability for relaxation.
Growth in the number of individuals playing the game of golf provides an incentive for manufacturers of golf equipment, which includes golf clubs, golf balls, and golf shoes, to improve upon the various features and characteristics of golf equipment. In general, golf equipment has evolved over time to provide enhanced performance and suitability for a wide range of playing abilities and styles. Golf club shafts, for example, were originally fashioned from wood and are commonly formed of metal or graphite materials today. Golf balls originally included a wound, twine core and a balata rubber cover. Modern golf balls, however, may incorporate a solid core formed of polybutadiene, titanium, nickel, or cobalt, and a cover formed of ionomeric resin, surlyn, or polyurethane. Similarly, advances in golf shoe outsoles are of particular interest to sporting goods manufacturers, especially with respect to enhancing performance by insuring controlled contact with the ground while permitting the body to correctly pivot for purposes of swinging a golf club.
A proper golf club swing involves a side-to-side twisting motion that coordinates movement of the arms, torso, hips, legs, and feet of the golfer. Initially, the weight of the golfer is uniformly distributed over each foot. As the golfer begins the back swing, the driving foot, which is positioned furthest from the flag, tends to experience an increased vertical force and tends to rotate laterally outward in the forefoot region and medially inward in the heel region. During the back swing, the driving foot acts as a brace and counters rotation of the torso, hips, and legs. Accordingly, a majority of the weight of the golfer shifts to the driving foot during the back swing such that the stabilizing foot, which is positioned closest to the flag, supports only a small portion of the weight of the golfer. During the down swing, the golfer""s weight is shifted from the driving foot to the stabilizing foot, which has a tendency to rotate in a manner that is similar to the driving foot during the back swing. That is, the stabilizing foot tends to rotate laterally outward in the forefoot region and medially inward in the heel region.
Traditional golf shoes include a generally smooth outsole having a plurality of fixed or removable spikes that engage the ground and prevent each foot from slipping during the golf club swing. Although metal spikes are effective for preventing the feet from slipping, the spikes may damage putting greens, walkways, floors, and other surfaces that the golfer walks upon. Metal spikes may also pose a hazard to the golfer or other individuals. Many modern golf shoes, however, continue to incorporate metal spikes.
A modified golf shoe is disclosed in U.S. Pat. No. 4,885,851 to Peterson and includes an outsole with a flat, ground engaging surface and spikes positioned in the forefoot and heel regions. In addition, the outsole includes a plurality of supplementary protrusions distributed along a medial side of the right shoe and along the lateral side of the left shoe to aid a right-handed golfer. An opposite configuration is disclosed for a left-handed golfer. One purpose of the supplementary protrusions is to inhibit the shoes from slipping as the golfer shifts weight from the driving foot to the stabilizing foot during the golf swing.
Golf shoes may also be structured in a manner that considers the rotational motion of the feet during the various stages of the golf swing, as discussed above, in addition to the tendency for slipping throughout the golf swing. U.S. Pat. No. 6,016,613 to Campbell et al. discloses a golf shoe outsole with a plurality of polymer projections. The various projections are configured to extend outward in a radial geometry from a pivot point in the forefoot region and another pivot point in the heel region, thereby controlling the rotational motion of the feet during the various portions of the golf swing. In addition, the outsole may incorporate traditional metal spikes or modern polymer spikes.
The present invention is an article of footwear having an upper for receiving a foot and a sole structure attached to the upper. The sole structure includes an outsole with an exposed surface and a plurality of traction elements projecting from the exposed surface. The traction elements have an end portion located opposite the exposed surface and an undercut surface that extends between the exposed surface and the end portion to form an acute angle with the exposed surface. A forefoot portion of the traction elements are located in a forefoot area of the sole structure, and a heel portion of the traction elements are located in a heel area of the sole structure. The undercut surfaces of the forefoot portion are oriented to generally face a lateral side of the footwear, and the undercut surfaces of the heel portion are oriented to generally face a medial side of the footwear.
The undercut surfaces of the traction elements engage the ground and resist rotation of the footwear. When an individual stands on a compliant surface, such as turf, the traction elements will protrude into the ground such that the undercut surfaces contact the ground. As the foot rotates, the ground presses against the undercut surfaces and deforms the traction elements, thereby increasing the angle that the undercut surfaces form with the ground. The angle, however, generally remains acute such that the traction elements continue to remain securely engaged with the ground.
During the back swing portion of a golf swing, the driving foot tends to rotate laterally outward in the forefoot area and medially inward in the heel area. Similarly, the stabilizing foot tends to rotate laterally outward in the forefoot area and medially inward in the heel area during the down swing. By orienting the traction elements such that the undercut surfaces face the lateral side in the forefoot area and the medial side in the heel area, rotation of the feet during the various portions of the golf swing may be effectively controlled.
The traction elements may also be utilized to provide the individual with additional cushioning. As the individual walks, the traction elements deform such that the angle between the undercut surface and the exposed surface decreases. The deformation in the traction elements effectively attenuates impact forces and absorbs energy, thereby providing the individual with cushioning.